An important factor in integrated network utilization of multiple high speed digital communication links (e.g. satellite, light, microwave, broadband cable, etc.) is the planning of common control station facilities to permit "globally" coordinated and balanced use of network link resources. When the traffic includes digitized telephone signals it is also desirable to be able to conserve link channels; e.g. by TASI and echo cancellation. This is complicated if the connection path in the high speed network includes multiple links in tandem and further complicated if the telephone signals represent adaptively companded delta modulation since it is then necessary to maintain equal companding (step-size) levels at the remote companding stations serving the connection. Above all it is desirable to have modular link connection station facilities which can be expanded over a period of years to handle increasing traffic without requiring extensive re-work of existing components and control programs.
Due to cost/performance considerations station designs have been proposed which usually embody some but not all of these desirable attributes. The object of the present invention is to provide improved link connection apparatus having all of these capabilities and cost/performance effectiveness.
Apparatus according to the present invention comprises modular random access slot interchange memory units SIM/ICM providing buffered (or delayed) time interchange pairing associations variably between telephone/data line circuits and time channels of time compressed multiplex (TCM) links. A feature of the invention is that random access buffer spaces in each module are reserved for slot interchange of activity bits useful for control of TASI, echo suppression, companding levels of adaptively companded delta modulated telephone signals and network routing. Another feature of the invention is that the slot interchange units have timing and commoned (OR-dotted) connections for addressing and out-busing enabling k independent switching tiers to operate as one unified switching facility; whereby an exchange constructed from said aggregate is expandable in port termination capacity and switching range, from the range/capacity of one unit to that of k units with conservative cost/performance.
Station apparatus in accordance with the present invention also includes common controlled random access line group modules (LGM) and trunk group modules (TGM) for buffer storage of digital signals in passage between undivided line terminations of the station and time or frequency channels of multiplex link terminals of the station slot interchange connections.
Apparatus in accordance with the present invention is adaptive to be linked with multiplex analog/digital telephone signal conversion units, under common control.
Apparatus in accordance with this invention is arranged for simplified "vertical" aggregation of up to k tiers of storage and conversion modules into a unified exchange served through the dot-OR'd slot interchange. An ancillary feature is that a variety of link connections may be established over the aggregate slot interchange range; including line-to-line ("local" or "tandem"), line-to-link channel ("toll") and link channel-to-link channel ("toll-tandem").
Apparatus as just characterized utilizes reserved time interchange slots of the SIM/ICM units to bidirectionally pass activity status information relative to associated traffic information slots served by these units. Furthermore such activity information is or can be used in the station for: (a) telephone echo suppression; (b) amplitude control in circuits carrying adaptively companded telephone signals; (c) TASI; (d) prioritized freezeout of TASI overloads; (e) network routing; and (f) network load balancing.
When compared to a more primitive satelite link TASI system disclosed in U.S. Pat. No. 3,644,680 granted Feb. 22, 1972, to Amano et al, the present TASI organization is distinguished in that: (a) the present associations of lines and virtual channels (storage channels scanned by the controls for TASI allocation) are variable due to the time interchange switching; (b) the interchange switch is expandable to serve plural multiplex links with separate TASI masks in a unified connection exchange (the Amano et al patent does not appear to have considered the need for this); (c) the possibility of TASI overload is considered presently and handled by prioritized freezeout of active virtual channels despite severe time restrictions inherently affecting such action (the Amano et al patent appears to have ignored overload possibilities, which implies settling for less than peak efficiency in use of the TASI channels); (d) the present apparatus contemplates slot interchange switching of both traffic intelligence and activity bits used for TASI and echo suppression; (e) present apparatus provides line-to-line, line-to-TCM link and link-to-link connection options with selective TASI control of link connections and resulting benefits of link and load balancing efficiency and reduced blocking of call connections.
Another feature is that the TCM frame time presently employed (e.g. 6 milliseconds) is long by comparison to the interval between successive samplings of any telephone line port (e.g. 1/32 of 1 millisecond). Consequently line port samples can be buffered and transmitted in multi-sample blocks for reduced transmission overhead (high ratio of traffic bits to synch and TASI mask bits).
Another feature is that present slot interchange storage modules operate to pass information in small byte pieces at a cycling tempo suitable for completing local line connections with short interchange delays and long distance connections with longer interchange delays (but short relative to link propagation delays); so that echo suppression is not required on short and medium distance connections.
Another feature of the invention is that the subject digital exchange station apparatus comprises one or more digital switch modules which can be independently hooked up to line multiples and multiplex trunks in vertical tiers and yet operate as a unified exchange for connecting any line in any tier with any trunk channel in any tier.
Another feature is that connection (interchange) operations of the exchange can be controlled by erasably stored tables which provide preferred and alternate route selection possibilities and virtual connection association possibilities not restricted by any physical orderings of the lines and channels.
Another feature is that trunk channels can be used to full capacity without undue degradation of service, due to prioritized freezeout and network configuration control practices presently disclosed.
The foregoing and other aspects, features, advantages and objectives of the present invention will be more fully appreciated from the following description and claims.